Variable voltage lamp



y 1935- c. H; BRASELTON 2,007,921

VARIABLE VOLTAGE LAMP Filed Dec; 7, 1931 IN VENT OR Patented July 9, 1935'.

UNITED STATES PATENT OFFICE Chester 11. Braselton, New York, N. Y., assignor to Sirian Lamp Company, Newark, N. .L, a corporation of Delaware.

. Application December 7, 1931, Serial No. 579,590

7 Claims.

This invention relates to improvements in lamps, particularly in lamps designed for variable voltage use.

In lamps as now commonly used on automobiles 6 or other, vehicles having variable speedprime movers, difiiculties arise from the fact that the impressed voltage on the lamp is variable because of the variable speeds at which the generator supplying the current for the lamps is driven. 10 For example, while stated voltages for a lamp may be six volts, the generator voltage in an automobile may vary from six to ten volts, or higher, so that the filament of the lamp is subjected to operation at voltages and consequent temperatures 15 which tend to bring about a more rapid deterioration than if the voltage were maintained constant on the lamps at the most efficient value.

An important object of the-present invention is to provide a lamp equipped with means which '20 will tend to prevent variation of applied voltage to the lamp and which is independent of the source of current. Another object is to provide a type of variable voltage lamp which may be constantly operated at its most eflicient tem- 5 perature.

Another object is to provide acurrent control means for a lamp which also may function as a source of scattered light especially desirable in an automobile lamp bulb when the automobile 30 is travelling at its higher speeds.

Still another object is to provide a lamp which may be used in any circuit subject to variable voltages and for variouspurposes of illumination, or other radiation.

35 Various other objects will appear on consideration of the following description and of the accompanying drawing, in which Fig. 1 is a view of an automobile lamp equipped with control means;

40 Fig. 2 is a view of a modification of the showing of Fig. 1, the filament being of the type adapted to form a layer of ionized gases immediately adjacent thereto;

Fig. 3 is a detailed view of the filament of Fig. 2;

45 Fig. 4 is a view of an enclosed gas discharge lamp utilizing the control mechanism of this invention;

Fig. 5 is a detail showing the electrodes of the lamp of Fig. 4; and

50 Fig. 6 is a view of another modification of lamp construction to which my invention is applied.

Beferrin to the drawing, in Fig. 1 I have indicated a bulb Ill of glass or similar material, on the base of which is mounted a stem or sup- 55 port II, which is sealed to the lamp base so as to form a gas retaining container. Mounted on the support H are the standards l2, l3, and I4, and between the standards l2 and I3 are interposed the coiled series connected sections l and N5 of the tungsten filament. As indicated, the 5 sections I 5 and I6 are in the shape of an inverted V and the combined resistance of the filaments is such as to operate efliciently on a voltage of approximately six volts, or in other words, the voltage of the storage battery with which the start- 10 ing, lighting and ignition systems of automobiles are ordinarily equipped.

Interposed between the standards l3 and I 4 is a coil I 1 of resistance wire, which in this particular'invention is of iron. The lead-in wire I8 is connected to the support l2, and the lead-in wire I 9 to the support l4, and consequently the coil I1 is in series with the light emitting coils l5 and I6 and all the current which passes through the tungsten filament also passes through the iron coil II.

The resistance wire I! is specified as iron because of. the fact that the resistance of iron increases very rapidly with a temperature in the temperature range approximately intermediate 100 C. and 500 C., or, for example, the specific electrical resistivity of iron as given by Smithsonian Physical Tables varies from 17.8 to 21.5 between 985 C. and 196.1 0., whereas between 196.1 and 400, the resistivity varies from 21.5 to 43.3. This indicates a steeper gradient of increase of resistivity in the temperature range between approximately 100 C. and 500 C. This resistance may be readily secured by modifying the diameter of the coil or the length or both, in accordance with the specific requirements of the lamp. It is apparent that by the aid of this resistance l1 when the voltage is increased, a

higher resistance is interposed in the circuit which electrically tends to maintain the voltage across the light giving filaments approximately constant, and hence the lamp may operate at its highest efliciency and without constant variation in its light emission.

The embodiment of Fig. 2 diifers from that of Fig. 1 in which an ordinary length of bare drawn tungsten wire is employed as the light radiation element. In Fig. 2 I utilize a coil' of tungsten 26 which is coated with alkaline earth metal oxides 2|, such as those of barium, strontium and the like,-and which, when heated, become actively electron emitting. When a coated filament of thistype is placed in a bulb containing certain inert gases, such as those of-neon, argon, helium, nitrogen and the like, eitheralone or mixed together or mixed with certain metallic vapors such as those of mercury, caesium, rubidium, etc., and an electric'heating current passed through the filament, a layer of ionized gases forms about I the filament which, in itself, is a source of light emission and combines with the filament and its coating to give a highly luminous source of radiation.

In such a lamp it is of course desirable that the voltage be maintained approximately constant, since when the voltage drops below a predetermined amount, the luminous layer or halo about the filament disappears. Consequently, the utilization of the iron wire control resistance of this modification becomes essential in order to have a lamp of this type which will operate at its most efficient value and maintain a uniform luminosity. The method of mounting this lamp is similar to that shown in Fig. 1.

In Fig. 3 of the drawing I have illustrated, in detail, one method of applyinga coating to the heated coil. It should be understood, however, that a possibly more satisfactory and more practical method of applying the coating is to force it within the coil so that it has contact therewith on its interior rather than the exterior. Other means of bringing the coating into contact with the filament may also be used, such as a discontinuous coating, the coating surrounding each individual strand of the wire rather than spreading between the various turns of the coil.

In Fig. 4 of the drawing is illustrated an application of the control resistance to a different formof lamp. In this lamp within the bulb 39 mounted on the support 3| are standards 32, 33 and 34, and on the standard 43 is welded a tungsten rod 35, and on the standard 33 a length of tungsten 36, these rods 35 and 36 having adjacent ends 31 and 38, and covered with a coating 39, as indicated in Fig. 5, of alkaline oxide of the type which emit electrons when heated, such, for example, as barium oxide. Surrounding the electrodes 31 and 38 is a coil of tungsten wire 40, the ends of which are attached to the standards 32 and 33 so that a continuous current may be passed between these standards. It is apparent that the electrode space is enclosed by the coil 40.

The rod 36, as shown in Fig. 4, is extended outwardly beyond the standard 33, and between this extension and the standard 34 is connected the resistance wire 4| of iron or metal having similar characteristics. The dimensions of the iron wire are'such as to maintain a constant potential upon the coil 40, and at the same time 1518:); exceed the temperature of approximately In operation, when current is applied intermediate the standards 32 and 34 in the presence of an atmosphere of inert gases, such as those of argon, neon, helium, nitrogen, and the like, and with or without the various metal vapors, such as those of cwsium, mercury or rubidium, a gaseous discharge forms intermediate the electrodes 31 and 38, which is brilliantly white in color. The discharge is apparently retained in position and maintained in restricted form by means of the coil 40. The coil 40 also is an important source of illumination because of its high temperature, and combined with the arc discharge, forms a light emitting radiator of high frequency.

The function of the resistance element 4| in this particular embodiment of the invention, is similar to that shown in Fig. 2, t th t t that it is necessary that a predetermined voltage be maintained in order to maintain the gas discharge between the electrodes. When operating with a variable voltage, such as that as exists in an automobile generator, the discharge would not operate properly unless utilization was made of a controlling means, such as that hereinabove described.

In the modification of Fig. 1 is shown an iron wire or other resistance having a temperature coeflicient increasing more rapidly with temperature than tungsten. In the modification of Figs. 2, 4 and 6, however, the actively conducting gases imparts to the tungsten a temperature coefiicient differing from that of tungsten in a vacuum, and hence tungsten, as well as other resistances such as nickel, might be used.

Another lamp construction to which my invention is applicable is illustrated in Fig. 6. In this lamp there is provided a container 50 having a stem or support 5| provided with standards 52, 53, 54, and 55. Lead-in wire 56 connects to standard 52, and lead-in wire 51 connects to standards 53 and 55, as shown. Between the standards 52 and at their upper ends is connected the coiled conductor 58 which may be of tungsten and which is provided with a coating 59 either exteriorly, as shown, or interiorly, or in the shape of a homogeneous mixed filament containing electron emitting substances. Tubes and 6| are positioned end to end about the conductor 59, there being a small annular space between the adjacent ends which may vary but which in one instance is one thirty-second of an inch. This space may be either open or it may contain an annular strip of insulating material such as mica. The tubes 60 and GI preferablyhave coatings 62 of electron emitting substances. The tube 60 is supported on the standard 54 and the tube BI is supported on the standard 52.

Intermediate the upper portion of the standard 53 and a point on the standard 54 is a length of resistance wire 63 which is preferably of iron, although nickel or tungsten might be used, and the same having function of a ballast.

In operation, when a voltage is applied to the lead-in wires 56 and 51, current passes through the conductor 58 which heats up the coating 59 to a point where it emits electrons, whereupon the gases are ionized and the tubes 60 and GI, both by electronic and ionic bombardment, become heated to an extent that causes activation of the electron emitting coating thereon, the breakdown potential of the gap between the tubes 60 and GI being exceeded, the gases being made conductive by the electron emission. A discharge occurs about the gap, this discharge being in series with the ballast resistance 63 which becomes heated and tends, accordingly, to increase the resistance of the circuit and thus prevent a destructive fiow of current between the tubes 60 and BI. The gases used in this container are similar to those mentioned in connection with prior modifications.

While I have mentioned the application of coating either exterior or interior to the coil of the conductor, I have found that the coating material, such as various oxides of the alkaline metals, may be incorporated with the conducting substance. For instance, I may use thoriated tungsten; that is, a mixture of tungsten and: oxides of thorium or thorium metal produced by the chemical reaction of tungstic acid with thorium nitrate. Also, the coating materials may be applied in the shape of a core rod of angular shape, as, for example, a rod having a triangular section. Such form of the core limits the contact of the core against the interlor of the coil and thereby limits the amount of ionization which is desirable under certain-circumstances and uses. A wide variation of contacting surfaces may be made, as betweenthe core and the coil interior, in order to vary the amount of ionization when the coil is heated. I have found also that the general efliciency of the lamp may be increased, particularly the lamp incorporating Figs. 3 and 4, by the inclusion of vapors of calcium or caesium within the envelope, these vapors being introduced by means of solid pellets of the metal which are, subsequently vaporized by high tension induction applied externally to the envelope. The vapor facilitates the discharge, in

part, apparently bylowering the breakdown potential of the gases, and also by increasing the electron emission of the coating substance. Various other means of introducing additional metals may be employed, such as the actual transference of the vapors from an external container to the lamp, or by chemical reactions on the compounds placed within the lamp bulb. The vapor added,

electrodes the material substance of the coil may be increased. This effect may be also secured by placing a short length of coil 22 about the primary coil which contacts therewith, and which is connected to the support so that surges of current maybe taken care of without disrupting the filament. Under certain conditions it is desirable that straight wires should be used instead of the coils about the electrodes, and it is within the scope of the invention to eliminate the coils and utilize straight wires parallel to the electrode.

, I may also, particularly in the form of the .in-

vention shown in Fig. 4, find it desirable to insulate the standards 32 and 33 by coating the same with an insulating material or enclosing them in glass tubes or a similar non-conducting substance, this insulation extending from the electrodes down to the support 3|.

A feature of .the invention which should be referred to is that the presence of the ionized gases, in conjunction with the electron emission,

seems to restrain vaporization of the tungsten metal, and hence, there isless blackening of the bulb interior at the operating temperatures, and therefore more useful life of the lamp. Also, while the invention is described as applied to ordinary automobile lamp voltages, below 10 volts, it is equally useful at higher voltages, and for other types of lamps which are subjected to variable voltages. For example, the lamp may be operated at commercial voltages, such as Volts. v I i In the modification of Figs. 2, 4 and 6, where use is made of an ionizable gas, as a parallel conducting path to a metal circuit, in a lamp utilizing 110 volts, it may be expedient to divide the illuminant into sections, to each of which a lower voltage of 20 to 40, for instance, might be applied,

since I have found that under certain operating '0 nditions, and with certain materials, the filaentoperates better at lower potentials around those specified. *These filament sections may may be obtained by connecting a number of lamps in series, each lamp having a low normal voltage. Also, the pressure of the gas used may vary over wide limits depending on the gas, as well as the efiects desired. Where a halo of luminous gases close to the filament is wanted, the pressures should be higher.

While I have particularly emphasized the invention in connection with automobile lamps it is to be understood that the same type of lamp is applicable for use in any circuit where variable voltages are encountered.

Other modifications of the invention may be made, such as come within the scope of the claims hereinafter appended.

I claim as my invention: v

1. In an electriclamp the combination of a container, a support mounted therein, a. coil of refractory wire mounted on said support, a coating of electron emitting material having an emissivity equal to that of the alkaline earth metal oxides on said coil, a resistance wire connected in series with said coil, an atmosphere of inert gaseswithin the container having a pressure sufficient to confine the ionization of said gas to a well defined area in the region of said coil when said coil is raised to electron emitting temperature, and connections whereby "electric current is passed in series through said coil and wire, said resistance wire having arate of change of resistance per unit change of temperature greater than and in the same direction as the .refractory wire.

2. In an electric lamp the combination of a container, a support mounted therein, a coil of refractory wire mounted on said support, a coating of electron emitting material having an emissivity equal to that of the alkaline earth metal oxides on said coil, a resistance wire connected in series with said coil, an atmosphere of inert gases within the container having a pressuresufiicient to confine the ionization of said gas to a well defined area in the region of said coil when said coil.

is raised to electron emitting temperature, and connections whereby electric current is passed in series through said coil and wire, said gases including neon, said resistance wire having a .rate

of change of resistanceper unit change of temperature greater than and in the same direction as the refractory wire.

3. In a lampthe combination of a transparent container, a support mounted therein, a continuous coil mounted on said support, solid metal electrodes on said support within said coil, the ends of said electrodes being adjacent to but displaced -material having an emissivity equal to that of the alkaline earth metal oxides on said coil, means for maintaining a constant potential on said coil when a variable electrd-motive force is applied to the ends thereof, and an atmosphere of inert ionizable gases within said container and immersing said coil.

5. In an electric l 1 'p the combination of a container, a support mounted therein, a coil .of

refractory wire mounted on said support, electron emitting material having an emissivityequal to 4 that a the alkaline earth metal oxides mixed with the substance of the conductor forming a coil. a

resistance wire connected in series with said coil, an atmosphere of inert gases within the container having a pressure suflicient to confine the ionization of said gas to a well defined area in the region of said coil when said coil is raised to electron emitting temperature, and connections whereby electric current is passed in series through said coil' and wire, said resistance wire having a rate of change of resistance per 1mit change of temperature greater than and in the same direction as the refractory wire.

6. In an electric lamp the combination of a container, 9. support mounted therein, a refractory wire mounted on said support, said wire being adapted to emit electrons with a density equal to that of the alkaline earth metal oxides when heated, a resistance wire connected in series passed through said electron-emitting wire and said resistance wire, said resistance wire having a rate of change of resistance per unit change of temperature greater than and in the same di rection as the refractory wire.

'7. In an, electric lamp the combination of a container, a support mounted therein, a plurality of standards mounted on said support, a conductor intermediate to said standards, electron emitting material having an emissivity equal to that of the alkaline earth metal oxides incorporated in said conductor, two tubes surrounding said conductor and having closely adjacent ends providing gas discharge electrodes, a resistance wire in series with one of said tubes and another of said standards and in parallel with said coated conductor, and means for maintaining a discharge between said tubes when said tubes are heated by electronic bombardment from said conductor, said resistance wire having a rate of change of resistance per unit change of temperature greater than and in the, same direction as the conductor.

CHESTER H. BRASELTON. 

